Linear ultrasonic shear stress cutting blade

ABSTRACT

An ultrasonic horn for use with an ultrasonic surgical handpiece including a resonator comprises a linear cutting blade at the distal end of a horn body. The linear cutting blade includes adjacent side-by-side rows of teeth each of which includes a land through which ultrasonic waves are propagated outwardly from the distal end. The lands of the rows of teeth are angled so that the propagated ultrasonic waves of one plurality of lands intersects the propagated ultrasonic waves from the other row of lands. Shear stress fields are developed at the intersections of the ultrasonic waves that will perform the cutting function on target tissue. An irrigation arrangement is also disclosed.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/243,934, filed Aug. 22, 2016, now U.S. Pat. No. 10,799,260, which isincorporated herein by reference.

BACKGROUND

The invention relates generally to ultrasonic surgical devices, and moreparticularly to an ultrasonic cutting blade.

Devices that effectively utilize ultrasonic energy for a variety ofapplications are well known in a number of diverse arts. One of thesedevices is an ultrasonic horn used for the removal of tissue. TheAmpulla or Gaussian profile was published by Kleesattel as early as1962, and is employed as a basis for many ultrasonic horns in surgicalapplications including devices described in U.S. Pat. No. 4,063,557 toWuchinich, et al, 1977, and U.S. Pat. No. 6,214,017 to Stoddard, et al,2001 for use in ultrasonic aspiration. The Gaussian profile is used inpractice to establish and control the resonance and mechanical gain ofhorns. A resonator, a connecting body, and the horn act together as athree-body system to provide a mechanical gain, which is defined as theratio of output stroke amplitude of the distal end of the tip to theinput amplitude of the resonator. The mechanical gain is the result ofthe strain induced in the materials of which the resonator, theconnecting body, and the ultrasonic horn are composed.

A magnetostrictive transducer coupled with the connecting body functionsas a first stage of the booster horn with a mechanical gain of about2:1, due to the reduction in area ratio of the wall of the complexgeometry. The major diameter of the horn transitions to the largediameter of the Gaussian segment in a stepped-horn geometry with a gainof as large as about 5:1, again due to reduction in area ratio. Theuniform strain along the length of the Gaussian provides multiplicativegain of typically less than 2:1. Thus, the application of ultrasonicallyvibrating surgical devices used to fragment and remove unwanted tissuewith significant precision and safety has led to the development of anumber of valuable surgical procedures. Accordingly, the use ofultrasonic aspirators for the fragmentation and surgical removal oftissue from a body has become known. Initially, the technique ofsurgical aspiration was applied for the fragmentation and removal ofcataract tissue. Later, such techniques were applied with significantsuccess to neurosurgery and other surgical specialties where theapplication of ultrasonic technology through a handheld device forselectively removing tissue on a layer-by-layer basis with precisecontrol has proven feasible.

Certain devices known in the art characteristically produce continuousvibrations having substantially constant amplitude at a predeterminedfrequency (i.e. 20-36 kHz). Certain limitations have emerged in attemptsto use such devices in a broad spectrum of surgical procedures. Forexample, the action of a continuously vibrating tip may not have anadequate effect in breaking up certain types of body tissue, moreelastic tissue, bone, etc. Because the ultrasonic frequency is limitedby the physical characteristics of the handheld device, only the motionavailable at the tip provides the needed motion to break up a particulartissue. All interaction with the tissue is at the tip, some is purelymechanical, and some is ultrasonic. Some teach in the art thatinteraction with the tissue at the tip distal and is due only tomechanical interaction. To others, it is clear from experimental resultsthat acoustic power is propagated to the load to aid in tissuefragmentation, emulsification, and aspiration. In any case, the deviceshave limitations in fragmenting some tissues. The limited focus of sucha device may render it ineffective for certain applications due to thevibrations which may be provided by the handheld device. For certainmedical procedures, it may be necessary to use multiple hand helddevices or it may be necessary to use the same console for poweringdifferent handheld devices. [0006]

Certain devices known in the art characteristically produce continuousvibrations having substantially constant amplitude at a frequency ofabout 20 to about 55 kHz. Amplitude of transducer-surgical tip systemsdecreases with increasing frequency because maximum stress in thematerial of the horns is proportional to amplitude times frequency, andthe material must be maintained to an allowed fraction of its yieldstrength to support rated life in view of material fatigue limits. Forexample, U.S. Pat. Nos. 4,063,557, 4,223,676 and 4,425,115 disclosedevices suitable for the removal of soft tissue which are particularlyadapted for removing highly compliant elastic tissue mixed with blood.Such devices are adapted to be continuously operated when the surgeonwishes to fragment and remove tissue, and generally is operated by afoot switch.

A known instrument for the ultrasonic fragmentation of tissue at anoperation site and aspiration of the tissue particles and fluid awayfrom the site is the CUSA EXcel® Ultrasonic Surgical Aspirator (IntegraLifeSciences Corporation, Plainsboro, N.J.). When the longitudinallyvibrating tip in such an aspirator is brought into contact with tissue,it gently, selectively, and precisely fragments and removes the tissue.The CUSA® transducer amplitude can be adjusted independently of thefrequency and this amplitude can be maintained under load depending onreserve power of the transducer. In simple harmonic motion devices, thefrequency is independent of amplitude. Advantages of this uniquesurgical instrument include minimal damage to healthy tissue in a tumorremoval procedure, skeletoning of blood vessels, prompt healing oftissue, minimal heating or tearing of margins of surrounding tissue,minimal pulling of healthy tissue, and excellent tactile feedback forselectively controlled tissue fragmentation and removal.

In an apparatus that fragments tissue by the ultrasonic vibration of atool tip, efficiency of energy utilization is optimized when thetransducer which provides the ultrasonic vibration operates at resonantfrequency. The transducer and surgical tip design establishes theresonant frequency of the system, while the generator tracks theresonant frequency and produces the electrical driving signal to vibratethe transducer at the resonant frequency. However, changes inoperational parameters, such as changes in temperature, thermalexpansion and load impedance, result in deviations in the resonantfrequency. Accordingly, controlled changes in the frequency of thedriving signal are required to track the resonant frequency. This iscontrolled automatically in the generator.

Conventional ultrasonic surgical aspirating tips employed in surgery formany years typically present a longitudinally vibrating annular surfacewith a central channel providing suction or aspiration, which contactstissue and enables fragmentation via described mechanisms of mechanicalimpact (momentum), cavitation, and ultrasound propagation. Mechanicalimpact may be most useful in soft tissue and cavitation clearlycontributes to the fragmentation of tenacious and hard tissue insituations where liquids are present and high intensity ultrasoundexceeds the cavitation threshold.

Ultrasound propagation is concerned with the transmission of pressureacross the boundary of a surgical tip and tissue, which leads to thepropagation of pressure and, perhaps more importantly, particledisplacement. Acoustic impedance is the total reaction of a medium toacoustic transmission through it, represented by the complex ratio ofthe pressure to the effective flux, that is, particle velocity timessurface area through the medium. As discussed in the classic text ofKrautkramer J. and Krautkramer H., ULTRASONIC TESTING OF MATERIALS,Berlin, Heidelberg, N.Y., 1983, for the case of a low to high acousticimpedance boundary, it may seem paradoxical that pressure transmittedcan exceed 100% but that is what results from the build-up of pressurefrom a low to high acoustic impedance boundary. In the case of a high tolow acoustic impedance mismatch, such as with a high impedance titaniumultrasonic horn to low impedance fibrous muscle, soft tissue, or water,the pressure transmitted decreases (e.g., less than 15% for titanium tofibrous muscle) and particle displacement increases (e.g., as great as186% for titanium to muscle).

Conventional ultrasonic surgical aspirating tips have been found to beefficient in the removal of soft tissue, and with emergent bone tips,applicable to the removal of hard tissue; however, some fibrous,elastic, and tenacious tissues persist in difficulty of removal. It hasbeen found that using such conventional ultrasonic horns and devicesthat employ only the effects of intensification of ultrasound orsharpened edges to remove bovine fibrous muscle tissue, leaves a fibrouselastic skeleton. Thus, there remains a need for ultrasonic surgicaldevices with innovative aspiration tips that allow for more effectiveremoval of fibrous tissue via the enhanced utilization of ultrasoundfragmentation effects.

It is known that materials often fail, fracture, tear, or rupture, morereadily as a result of a shear force rather than in tension orcompression. Common examples include paper, garden bushes, hair, cloth,steel shear bolts or pins, and collagenous materials. A thin fibroussheet of paper can be pulled or snapped with a greater tension force,but it can much more easily be ripped by the fingers applying lightforces in opposite directions (shear). Likewise, scissors readily cutpaper by employing a shear force concentrated by opposing edges of thescissors. Studies of mechanical behavior of materials have shown thatbiologic tissue is viscoelastic material, meaning that it has atime-dependent stress-strain relationship. The effect of the strain rateon the material is critical to causing fragmentation. The ultrasonichorn of the present invention evolved from imagining innovative ways ofintroducing scissor or shear ultrasonic effects with a surgicalaspirating tip.

Cutting living bone in the field of orthopedics is performed in manyprocedures. Such procedures include grafting healthy bone into areasdamaged by disease, or the correction of various congenitalabnormalities. Mechanical bone saws have been traditionally used. Whilethey are functional, there are disadvantages. With some it is difficultto initiate a cut. A cut must start from an edge or from a startinghole. When a rotary blade is used, binding of the rotary blade can occurunless the blade is moved in a straight line through the bone. Creatinga curved cut can be limited by the configuration of the blade that ischosen. The use of relatively thick blades is likely to remove viableundamaged bone during the cutting procedure, which is undesirable. Agoal in many procedures is to cut a width that is as small as possible.

Also, mechanical saw blades can develop heat during use which can causenecrosis of the surrounding tissue, another very undesirable effect.Heat can lessen the strength of the bone also. Irrigation with coolingfluid is often used when cutting bone and this can assist in avoidingnecrosis. However, it is difficult to uniformly cool the tool.

One advance in the field has been the use of ultrasonic surgicalinstruments to take the place of traditional bone saws or scalpels.These devices have proven to be superior to the traditional saws inseveral aspects, such as the thinner size of their cutting tool, lowerednoise levels, and their ability to more easily make complex geometriccuts. Since ultrasound energy dissipates in soft tissue (dura, nerves,vascular structures, etc.) this device is the ideal tool for boneremoval in critical areas. However, some of those available today stillrely at least part of the tool having a saw blade that can mechanicallycut the bone. This creates heat which can be detrimental to the targetbone as described above. The ultrasound tools are able to effectivelyuse irrigation during the cutting process which will lessen the amountof heat transferred to viable bone tissue.

Soft tissue has elastic properties that allow it to deform and reboundwithout failure to its integrity. Osteotomies can be performed in closeproximity to delicate structures. Tissue response to the ultrasoundaction differs by tissue density, collagen content, blade pressure, andexposure time. Integrated and continuous irrigation is used tocompensate for thermal effects.

Another need has been shown for an ultrasonic cutting blade that is ableto cut laterally (also referred to as “transversely”), that is, in adirection substantially perpendicular to the axis of the blade, and thussubstantially perpendicular to the direction of propagation ofultrasonic compression waves, in addition to cutting in a forward ordistal direction away from the user. A further need that exists is foran ultrasonic cutting blade that, in addition to cutting in a forward ordistal direction away from the operator of the instrument, is able tocut rearward, that is in a proximal direction towards the operator.

Hence, those skilled in the art have recognized a need for an improvedsurgical device and method with innovative aspiration tips that allowfor more effective removal of fibrous tissue via the enhancedutilization of ultrasound fragmentation effects. There is also arecognized need for an ultrasound device with provides irrigationcooling to protect tissue. A further need has been identified for anultrasound cutting device that allows more effective removal of fibrousand tenacious tissues. Yet a further need has been identified for acutting device that can be used in different directions. The presentinvention fulfills these needs and others.

SUMMARY OF THE INVENTION

Briefly and in general terms, the present invention is directed to anapparatus and an associated method of fragmenting and removing targettissue by the introduction of shear stress and the utilization of highstrain rates associated with ultrasound. In more detailed aspects, theinvention is directed to an ultrasonic horn configured for use with anultrasonic surgical handpiece having a resonator that generatesultrasonic waves, the ultrasonic horn comprising a body member having aproximal end, a distal end, and a longitudinal axis, the proximal endbeing adapted to connect to the handpiece and receive ultrasonic wavesfrom the handpiece, and the body member configured to conduct thereceived ultrasonic waves to the distal end, an ultrasonic blade locatedat the distal end, the ultrasonic blade being non-annular and having alinear cutting surface on which are located two teeth positionedadjacent each other, each tooth having a root located at the cuttingsurface and a land located outward from the cutting surface, each landconfigured to propagate ultrasonic energy outwardly from the distal end,and wherein the land of the first tooth and the land of the second toothare located and oriented in relation to each other so that therespective ultrasonic energy propagated outwardly by both landsintersect to create a shear stress field.

In more detailed aspects, the linear cutting surface has a first widthon which the adjacent teeth are located, and wherein the blade hasmaterial under the linear cutting surface that is undercut whereby awidth of the blade at the undercut is less than the width of the bladeat the cutting surface. The first tooth is located on the cuttingsurface so that the first land is extending in the distal direction. Theroots of the first and second teeth are transversely aligned with eachother across the longitudinal axis at the cutting surface. An angle ofthe land of the first tooth and an angle of the land of the second toothare different. The roots of the first and second teeth are offset fromeach other across the longitudinal axis at the cutting surface. Theangle of the land of the first tooth and the angle of the land of thesecond tooth are opposite angles.

In yet another aspect, the first tooth is located at the cutting surfaceand oriented at an angle to the longitudinal axis so that ultrasonicenergy propagating from the land of the first tooth intersectsultrasonic energy propagating from the face of the second tooth so thata shear field is located transverse to the longitudinal axis.

In further aspects, the first tooth is located in a first linear row ofa plurality of teeth that is located at the cutting surface, each of theteeth in the first row of teeth having a root and a land wherein thelands have angles, the second tooth is located in a separate secondlinear row of a plurality of teeth that is located at the cuttingsurface adjacent the first row of teeth, each of the teeth in the secondrow of teeth having a root and a land wherein the lands have angles, andwherein the angles of the lands in the first and second rows areselected to be different so that ultrasonic energy propagating throughthe rows of teeth and outwardly through the lands will intersect toresult in a plurality of shear fields. The lands of the teeth in thefirst row extend in the distal direction and the lands of the teeth inthe second row extend in the proximal direction. The roots of the teethin the first row are aligned transversely with the roots of the teeth inthe second row and the lands of the first row have a different anglefrom the lands in the second row.

In other more detailed aspects, the first and second rows are parallelwith the longitudinal axis and are positioned on either side of thelongitudinal axis in forming the linear cutting surface of the blade.The roots of the teeth in the first row are offset from the roots of theteeth in the second row and the lands of the first row have the same butopposite angle in respect to the lands in the second row.

In additional aspects, there is provided an ultrasonic horn configuredfor use with an ultrasonic surgical handpiece having a resonator thatgenerates ultrasonic waves, the ultrasonic horn comprising a body memberhaving a proximal end, a distal end, and a longitudinal axis, theproximal end being adapted to connect to the handpiece and receiveultrasonic waves from the handpiece, and the body member configured toconduct the received ultrasonic waves to the distal end, and anultrasonic blade located at the distal end, the ultrasonic blade beingnon-annular and having a linear cutting surface on which are located twolinear rows of teeth, each row having a plurality of teeth, the rowsbeing positioned on either side of the longitudinal axis adjacent eachother, each tooth having a root located at the cutting surface and aland located outward from the cutting surface, each land configured topropagate ultrasonic energy outwardly, wherein the lands of the firstrow of teeth and the lands of the second row of teeth are located andoriented in relation to each other so that the respective ultrasonicenergy propagated outwardly by the lands of one row intersect with theultrasonic energy propagated outwardly by the lands of the other row tocreate shear stress fields.

In related detailed aspects, the locations of the roots in the firstlinear row of teeth are offset from the locations of the roots in thesecond linear row of teeth; and the angles of the lands in the first rowof teeth are opposite the angles of the lands in the second row ofteeth. The locations of the roots in the first linear row of teeth arealigned with the locations of the roots in the second linear row ofteeth, and the angles of the lands in the first row of teeth aredifferent from the angles of the lands in the second row of teeth.

In method aspects in accordance with the invention, there is provided amethod of creating a shear stress field with ultrasonic energycomprising conducting ultrasonic energy through a body member from aproximal end of the body member to a distal end of the body member, thebody member having a longitudinal axis and propagating the conductedultrasonic energy outwardly from the distal end of the body memberthrough a first tooth and a second tooth that are both mounted to acutting surface of a non-annular linear blade located at the distal endand are positioned adjacent each other, each tooth having a root locatedat the cutting surface and a land located outward from the cuttingsurface, wherein the step of propagating comprises propagatingultrasonic energy outwardly by each land in a direction that intersectspropagated energy by the other land to thereby form a shear stressfield.

In more detailed method aspects, the propagating step further includespropagating the conducted ultrasonic energy outwardly from the distalend of the body member through lands of a first row of teeth and throughlands of a second row of teeth, both rows of teeth being locatedseparately at the non-annular, linear cutting surface and are positionedadjacent each other in a side-by-side arrangement. The lands of one rowof teeth have a first angle and the lands in the other row of teeth havea second angle that is opposite the first angle.

Other features and advantages of the present invention will become moreapparent from the following detailed description of the invention, whentaken in conjunction with the accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the presently disclosed shear stress ultrasonic hornhaving a cutting blade are described herein with reference to theillustrative drawings, in which:

FIG. 1 is a perspective view of an ultrasonic horn in accordance withaspects of the present invention in which the horn includes an extensionmember, an elongated member, and a distal end having a linear cuttingblade of a particular configuration for establishing shear stress intarget material, and further includes an adapter at its proximal end forconnection with an ultrasonic energy source;

FIG. 2 presents a perspective view of an ultrasonic horn similar to FIG.1 having the cutting blade located at its distal end, the horn alsoshowing actual connection to an ultrasonic energy generator at itsproximal end;

FIG. 3 shows a general cross-sectional view of the horn embodiment ofFIG. 1 showing a channel formed completely through the horn includingthe distal tip cutting blade in this embodiment, the channel beingusable for aspiration;

FIG. 4 is a side view of the horn of FIG. 1 showing further detail ofthe adapter configuration at the proximal end of the horn and showing indashed lines the channel formed through the entire length of the hornthat is usable for aspiration;

FIG. 5A is a perspective view of an embodiment of a shear stressultrasonic linear cutting blade mounted at the distal end of the hornsof FIGS. 1 and 2 showing a pair of adjacent separate rows of teethlocated at the cutting surface of the cutting blade, each tooth having aland with the lands of one row having the same but opposite angle inrespect to the lands of the other row with the roots of the teeth of onerow being offset in respect to the roots of the teeth of the other row,the blade being undercut below the cutting surface, and further showingthe distal opening of the internal aspiration channel;

FIG. 5B is a side view of the shear stress ultrasonic cutting blade ofFIG. 5A showing one row of teeth in the front and what can be seen ofthe second row of teeth in the back;

FIG. 5C is a front view of the shear stress ultrasonic cutting blade ofFIGS. 5A and 5B showing the opening of the aspiration channel and theundercut of the blade under the cutting surface;

FIG. 5D is a top view of a cutting blade in accordance with aspects ofan embodiment of the invention of showing the roots and lands of bothrows of teeth, in particular showing that the roots of the teeth of onerow are offset from the roots of the teeth of the adjacent row wherebythe angles of the lands can be opposite each other to form shear stressfields;

FIG. 5E is a top view of the cutting blade of in accordance with aspectsof an embodiment of the invention of showing the roots and of both rowsof teeth are aligned but with the lands of one row having a differentangle from the lands of the adjacent row to form shear stress fields;

FIG. 6A is a perspective view of a different embodiment of a shearstress ultrasonic cutting blade mounted at the distal end of the hornsof FIGS. 1 and 2 similar to that of FIG. 5A except that the teeth ofthis embodiment are all formed by triangular cuts with the rows beingoffset from each other;

FIG. 6B is a side view of the shear stress ultrasonic cutting blade ofFIG. 6A showing one row of teeth in the front and what can be seen ofthe second row of teeth in the back;

FIG. 6C shows a different embodiment of an ultrasonic horn having anshear stress ultrasonic cutting blade mounted at the distal end of abody member as in other figures but in this figure there is also shownan irrigation system comprising a flue surrounding part of the horn justproximal to the cutting blade, the flue being open at its distal end sothat irrigation fluid will be distributed down the blade by gravity inthis embodiment;

FIG. 7 is a basic diagram showing the operation of Snell's law at theinterface of two different materials, one of which is the material ofthe shear stress ultrasonic cutting blade of the ultrasonic horn and theother of which is the material of target tissue;

FIG. 8 is a schematic diagram showing the refraction of ultrasonicenergy from a land of a tooth of the cutting blade located at the distalend of an ultrasonic horn, the land being oriented at a first angle of+45°;

FIG. 9 is a schematic diagram showing the refraction of ultrasonicenergy from a land of a tooth of the cutting blade located at the distalend of an ultrasonic horn, the land being oriented at a second angle of−45° (which is opposite the first angle);

FIG. 10 is an illustration of the propagation of a shear stress fieldthrough adjacent cells located about the apex of the land members ofFIGS. 8 and 9 that results when the refracted waves of the first landmember (FIG. 8) are coupled with the refracted waves of the second andadjacent land member (FIG. 9);

FIG. 11 is a graph of the ultrasonic horn radius versus horn length fora target frequency of 36 kHz shown in area function of the Gaussianshape; and

FIG. 12 presents a diagram of the shape of an ultrasonic horn.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Turning now in more detail to the figures, in which like referencenumerals designate like or corresponding elements among the severalviews. As used herein, the term “distal” refers to that portion of theinstrument, or component thereof which is farther from the user whilethe term “proximal” refers to that portion of the instrument orcomponent thereof which is closer to the user during normal use. Theterms “ultrasonic horn,” “ultrasonic aspirating tip,” “aspirating tip,”“ultrasonic surgical tip,” and “surgical tip” are used hereininterchangeably.

Referring now to FIG. 1 in more detail, there is shown an ultrasonichorn 100, in accordance with one embodiment of the present disclosure.The ultrasonic horn is adapted for use in an ultrasonic surgical systemhaving an ultrasonic handpiece. An example of such an ultrasonicsurgical system is disclosed in U.S. Pat. No. 6,214,017 to Stoddard etal., the entire contents of which are incorporated herein by reference.Alternatively, the ultrasonic horn 100 may be adapted for use with theultrasonic surgical system disclosed in U.S. Pat. No. 4,063,557 toWuchinich et al., the entire contents of which are incorporated hereinby reference.

The ultrasonic horn 100 of FIG. 1 includes a proximal end 104 and adistal end 106. At the proximal end the horn comprises an adapter 102that includes, extending from the proximal end 104 towards the distalend 106, a shaft 108, a threaded member 110, and a flange 112terminating at the distal end 106. The flange 112 includes a leadingedge 114.

The proximal end 104 of the adapter 102 is configured to connect theultrasonic horn 100 to an ultrasonic handpiece or resonator. Referringalso now to FIG. 2, the connection of an ultrasonic horn to a resonator140 is shown. FIG. 2 shows a horn 101 similar to the horn 100 of FIG. 1with the exception that the horn 101 of FIG. 2 is curved at an angle ofapproximately 13°. The base designs of such horns include both curvedand straight surgical tips; i.e. the profiles may be the same. Thesurgical curved tips are bent on a mandrel following machining. The bendcan be about 13° or less.

Curved surgical tips are often preferred because the handpiece is movedout of the field of view of the microscope used by the surgeon viewingthe distal end. The curve in the embodiment of FIG. 2 is formed in anextension member 120 of the horn, as described below in further detail.

The resonator 140 is connected to the adapter 102 of the horn through aconnecting body 142 in this embodiment. As used herein, the term“resonator” refers to what is often referred to in the literature as anultrasonic handpiece. The resonator is typically a laminated core-stackof Permanickel. Those skilled in the art will recognize that thethreaded member 110 is identified herein in one embodiment as anexternally threaded member for connection to internal threads of theconnecting body 142 and/or to an ultrasonic resonator 140 but that otherconnection types can be implemented to connect to the connecting bodyand/or ultrasonic resonator. Such connection types include but are notlimited to welds, socket couplings, and compression couplings. Becausesuch resonators and connections are well known to those skilled in theart, no further details are provided here.

The ultrasonic horns 100 and 101 both include an extension member 120having a proximal end 122 that coincides with the flange 112 of theadapter 102. The extension member 120 also has a distal end 124. Thehorn further comprises an elongated member 130 with a distal tip 132 atthe distal end 106 of the horn. The distal end 124 of the extensionmember terminates in a transition segment 134 to the elongated member130 in this embodiment. The proximal end 136 of the elongated member islocated at the distal side of the transition segment 134 while thedistal end of the extension member is located at the proximal side ofthe transition segment. The distal end of the elongated member 130 isconfigured as the distal tip 132.

The connecting body 142 is configured to connect the resonator 140 tothe horn 101 so that ultrasonic energy may be applied to the horn andconducted to a target site. In one embodiment, the resonator 140includes a magnetostrictive transducer, although other transducer typescan be included such as a piezoelectric transducer. The resonator 140 issupplied power from a power generator (not shown) such that theresonator 140 operates at a target frequency, e.g., in the range ofabout 23,000 Hz (23 kHz), 36,000 Hz (36 kHz) or other. Utilizing apiezoelectric transducer will provide similar ultrasonic properties andalternate frequencies for higher stroke and power (e.g., 23 kHz and 24kHz devices). It is important to note that use of alternativetransducers or ultrasonic frequencies will not substantially deviatefrom the innovative principles of the shear stress ultrasonic horndisclosed herein. In one embodiment, the ultrasonic horns 100 and 101are made of titanium, although other materials such as stainless steelmay be used. In a preferred embodiment, the titanium ultrasonic horn isnitride coated to improve hardness and improve wear resistance.

As best seen in FIG. 3, which is a longitudinal cross-sectional view ofthe ultrasonic horn 100 of FIG. 1, an internal channel 146 is formedlongitudinally through the entire horn, i.e., from the distal end 106 tothe proximal end 104. The channel terminates in the connecting body 102,and does not continue into the resonator (not shown). In someembodiments, the channel may be coupled to a side port or other deviceto introduce fluid into the channel (irrigation) or withdraw fluid fromthe channel by means of suction or vacuum (aspiration). In someimplementations, the central channel supports aspiration or suction oftissue as it is broken into particles by the horn. The internal channelcan provide suction when connected with a vacuum source at the console.The suction can also be used to control the position of target tissue.For example, suction may be used to draw target tissue to the distal end160 of the horn for coupling and contact to the tissue for efficientfragmentation. The internal channel shown and described herein may alsobe used to aid in cooling, where irrigation liquid is caused to flowthrough the channel.

The internal channel 146 also affords greater mechanical gain for thehorn 100 and 101 because the gain is dependent on the reduction in arearatio of the thin walls. A purpose of the internal channel 146 is tosupport gain for surgical tips with the cutting blade distal end 160.

Referring now to FIG. 4, a side view of the ultrasonic horn 100 of FIG.3 is shown with only the channel 146 shown in dashed lines. The adapter102 is also shown. As is clearly shown in the dashed lines, the internalchannel 146 is also formed within the adapter 102 and throughout theremainder of the horn 100.

In FIGS. 1 through 4, the horn is shown as being elongated. This is notmeant to be limiting but only an embodiment. In other embodiments, thehorn may not be elongated depending on the requirements of theapplication. As referred to herein, the part of the horn proximal to thedistal end is referred to as a body member.

Referring now to FIG. 5A, there is shown a perspective, more detailed,view of an embodiment of a shear stress ultrasonic cutting blade 160that is mounted at the distal end 106 of the horns 100 and 101 of FIGS.1 and 2. FIG. 5A shows a configuration of features used to create shearstress in target tissue. In this embodiment, a pair of adjacent, butseparate, rows of teeth 202 and 204 are provided to form the cuttingblade 160. Each of the rows has a plurality of teeth lined up inparallel to the longitudinal axis 162 of the cutting blade in thisembodiment. Each tooth in this embodiment has two lands with a peak inbetween. Each tooth also has two roots, one at the base of each land ofthe tooth. As an example, tooth 205 of the first row 202 of teeth has adistal land 206 and a proximal land 208 with a peak 207 in between at aposition outward from the cutting surface 214. Two roots 216 and 218 ofa single tooth 205 in the first row 202 are shown in FIG. 5B. Each ofthe teeth in the first row have like features.

Each of the teeth in the second row 204 of FIG. 5A also have likefeatures with a distal land 210, a proximal land 212, and a peak 220 inbetween the two lands. Each tooth also has two roots (not shown) at thebottom of each land, which is at the cutting surface 214.

Referring briefly to FIG. 5C, a front view of the cutting blade 160 isshown. The blade includes a cutting surface 214 at which the rows ofteeth 202 and 204 are located. The remainder of the blade is undercut222 so that it will not cause the remainder 224 of the blade 160 to bindwhen cutting target tissue is being performed.

Referring back to FIG. 5B, ultrasonic energy is conducted through thehorn 100 to the distal end 106. That ultrasonic energy is propagatedoutward from the horn through the lands of both rows 202 and 204 ofteeth. Adjacent lands in this figure have different angles, that is, aland in the first row 202 is adjacent a land in the second row 204. Boththe distal lands of the adjacent teeth and the proximal lands of theadjacent teeth will have different angles. This is because the roots 216of the teeth 218 of the first row 202 are aligned with the roots 226 and228 of the teeth of the second row 204 which can be seen in FIG. 5D.However, the location of the peaks are different. In this embodiment,the peaks 207 of the teeth in the first row is centered and both thedistal and proximal lands are at an angle of 45° to the cutting surface214. However, the angles of the lands of the teeth in the second row aredifferent than those of the first row. The peaks 236 of the teeth in thesecond row 204 are placed so that the distal land 210 has an angle of60° with the cutting surface and the proximal land 212 has an angle of30°. However the angles of both the distal land 206 and the proximalland 208 in the first row 202 is 45°. That results in a difference inangle between the ultrasonic energy propagating from both sets ofadjacent lands of 15°. The propagating ultrasonic energy will intersectat those particular angles.

In FIG. 5B, the ultrasonic energy propagating 300 from the distal landof the most distal tooth of the second row will produce shear waves withthe energy propagating 302 from the distal land of the most distal toothin the first row when undergoing a longitudinal motion front stroke.Likewise the ultrasonic energy propagating 304 from the proximal land ofthe most distal tooth of the second row will produce shear waves withthe energy propagating 306 from the proximal land of the most distaltooth in the first row when undergoing a longitudinal motion backstroke.

Using ultrasonic shear geometry to provide a cutting device thatfunctions similarly to a saw or scalpel would be expected to haveimproved efficacy relative to existing devices. A cross-cut wood saw hasteeth that enable efficient cutting both with or across the grains ofwood. The teeth of a cross-cut saw are protruded, or bent off the centerline. In the embodiment of FIG. 5A, shear stress is promoted by havingthe rows of teeth next to each other with an angle of a land in one rowbeing next to a land of another angle located in the adjacent row, withadjacent rows of teeth, with lands of different angles.

These rows could be machined separately and brazed or silver soldered toan ultrasonic horn, or perhaps the horn can be machined as a contiguoussolid body using an EDM (Electrode Discharge Machine) mask. It isbelieved by the inventors that the shear geometry can be powered by astepped horn and perhaps a Gaussian horn. It is also believed that aripple wave perpendicular to the teeth could be promoted to give theeffect of protruding them relative to the longitudinal motion(transverse similar to a cross-cut).

FIG. 6A is a perspective view of a different embodiment of a distal tipcutting blade 250 mounted at the distal end of the horns of FIGS. 1 and2 similar to that of FIG. 5A except that the teeth of this embodimentare all formed by triangular cuts with the rows being offset from eachother. The ultrasonic shear stress cutting blade 250 has the sametriangle cuts for all teeth, both first row 252 and second row 254. Inorder to make angular differences between the angles of the lands in thefirst row and the lands in the second row, the root positions and peakpositions are offset. In this embodiment, the peaks 270 of the teeth inthe second row align with the roots 272 of the teeth in the first row.Thus the angular difference is 90° between all adjacent distal andproximal lands. This is shown if FIG. 6B where the energy propagatedfrom the distal land 256 of the first row intersects the energypropagated from the proximal land 266 of the second row. FIG. 5Epresents a view of the arrangement of the roots of the teeth of thefirst row being offset from the roots of the teeth in the second row.

In FIG. 6B, the ultrasonic energy propagating 310 from the distal landof the most distal tooth of the second row will produce shear waves withthe energy propagating 312 from the distal land of the most distal toothin the first row when undergoing a longitudinal motion front stroke. Theultrasonic energy propagating 314 from the proximal land of the mostdistal tooth of the second row will produce shear waves with the energypropagating 316 from the distal land of the most second most distaltooth in the first row when undergoing either a longitudinal motionfront or back stroke. Transverse motion may also be generated by theultrasonic energy of 314 and 316. The same is true for the ultrasonicenergy propagating 318 and 320 from lands in the front and back rows.Shear waves are created for front and back longitudinal strokes as wellas transverse motion. Transverse motion is shown by the axis Z in FIG.6A.

It has been found that adjacent lands of opposite angles promoterefracted longitudinal waves propagating in different directions at theinterface to the tissue to establish shear forces. Refractedlongitudinal waves of different directions produce a shear stress field,especially at the intersection of opposite angled lands 266 and 256, andthis shear stress enhances fragmentation and the removal rate of fibroustissue.

It will be noted that the teeth 274 and 276 at the ends of the first row252 are truncated while the teeth in the second row are full in theembodiment shown in FIGS. 6A and 6B.

FIG. 6C shows a different embodiment of an ultrasonic horn 280 having acutting blade 282 mounted at the distal end 284 as in other figures, butin this figure there is also shown an irrigation system 286 comprising aflue 288 surrounding the part of the body 290 of the horn just proximalto the cutting blade, the flue being open 292 at its distal end so thatirrigation fluid will be distributed down the blade by gravity. A feedtube 294 is used to conduct coolant to the flue from a source (notshown) at the proximal end 296 of the body 290. A tube for aspiration298 is also shown at the proximal end of the body 290.

In the figures, the distal lands have been called “distal” because theyface in the distal longitudinal direction. The rows shown in the figuresare linear and not annular. Likewise, the proximal lands have beencalled “proximal” because they fact in the proximal longitudinaldirection. In the embodiments shown, the rows of teeth are touching eachother although they are termed to be separate rows. The peaks of thelands are shown in the figures as being sharp but depending on theiruse, they may be blunted.

FIGS. 5D and 5E are top views of the relative positioning of the teethbetween rows. These are but two embodiments. The alignment of offset ofthe teeth in one row to the teeth in another row can be altered inaccordance with the application of the cutting blade. The angles of theteeth in both rows can be set to achieve different angles to develop theshear stress fields as desired.

It should be noted that the relative positioning between the teeth ofone row to the teeth of another row can be selected as desired toachieve the cutting results needed. Additionally, although shown in theembodiments as having only two rows of teeth, the cutting blade may havemore than two rows, as is needed for the purpose at hand.

It is known that the angle of refraction of the longitudinal wave can beideally calculated based on Snell's Law, and it is dependent on theincident angle and difference in acoustic velocity of titanium (thematerial of the horn in one embodiment) and the medium or mediaencountered at the boundary, e.g., soft tissue, fibrous muscle, water,etc. An illustration of the ultrasonic horn to tissue interface foradjacent lands of opposite angles is provided in FIGS. 7-10 for anassumed dominantly directed extensional wave along the longitudinal axisof the surgical tip. For a +45° and −45° interface of the titanium lands166 and 167 of opposite angles to tissue 180. the refracted longitudinalwave angles were calculated for air, water, soft tissue, muscle, andbone employing representative material properties from the literature.Most pertinent, a 13° refracted longitudinal wave angle is calculatedfor titanium to muscle.

In FIG. 7, the basic principle of refraction is illustrated. Theultrasonic energy 172 is propagating in titanium 174 at an angle of 0°,to the ordinate axis 176. Upon reaching the boundary 178 (abscissa axis)with fibrous tissue 180, the ultrasonic energy 172 is refracted by 13°.Therefore 0₂=±13° as measured from the normal to the interface.

FIG. 8 presents a diagram of a titanium land 186 having an innerdiameter ID and an outer diameter OD. Ultrasonic energy 172 ispropagating through the land at an angle of Θ₁=+45° to the centerline162 through the land. Upon reaching the boundary 186 with fibrous tissue180, refraction occurs and the ultrasonic energy then has an angle ofΘ₂, with the centerline 162, where Θ₁≠Θ₂.

FIG. 9 presents a diagram of a titanium land 190 having the oppositeland angle than that of the land 186 in FIG. 7. The land 190 has aninner diameter ID and an outer diameter OD. Ultrasonic energy 172 ispropagating through the land at an angle of Θ₁=−45° to the centerline192 through the land. Upon reaching the boundary 186 with fibrous tissue180, refraction occurs and the ultrasonic energy then has an angle of Θ₂with the centerline 192, where Θ₁≠Θ₂.

FIG. 10 is a drawing showing the land 186 of FIG. 8 in front of the land190 of FIG. 9 with the refracted ultrasonic energy of each creating ashear stress field 198. Due to the adjacent lands 186 and 190 being ofopposite angles, there will be component waves causing shear 198.Refracted longitudinal waves of different directions produce a shearstress field, especially at the intersection of opposite angled lands,and this shear stress enhances fragmentation and removal rate of fibroustissue 180. Adjacent cells or particles 200 about the intersection ofthe lands could experience displacement or particle motion with 64° ofshear. It is important to note that due to the adjacent lands being ofopposite angles (in this case +45° and −45°), there will always becomponent waves propagating at opposite angles that will subject thefibrous tissue to shear stress.

In a preferred embodiment, the shear stress tip implementation ofadjacent opposite angled lands 186 and 190 does not compress tissue 180.Ultrasound energy 172 from adjacent opposite angled lands does notcancel due to destructive interference. However, opposing faces wouldcancel ultrasound energy due to destructive interference and would causecompression of tissue.

It has been found that although a shear wave component may exist and aidin fragmentation when coupled via solids, refracted longitudinal wavesexist and will couple even in liquid, such as water or saline solutionsupplied as irrigation liquid via a surgical tip flue or anotherchannel. Shear waves will not propagate directly in gases and liquids.Shear stress is not wholly or largely dependent on coupling of a shearwave, but rather would be promoted by refracted longitudinal waves ofopposite angles.

Increasing the angle to 60° from 45° between the lands 166, 167 and thetissue would typically increase shear angle but reduce transmittedparticle displacement. Reducing the land angle between the lands 166,167 and the tissue from 45° to 30° would reduce shear angle but increaseparticle displacement. Given that particle displacement calculatedexceeds 130% for angles from 30° to 60°, the selection of angle may bedominated by shear angle and ease of manufacturing. Alternative anglescould be selected without substantially deviating from the shear stresstip principle of operation.

FIG. 11 illustrates a shear stress tip profile 230. Area function of theGaussian is shown, and it influences the resonant frequency and themechanical gain. A blend is provided to a short straight section 232. Aflared exponential profile 234 of the home expands the wall thicknesssuitably for machining of the distal end of the shear stress tipcomprising a plurality of lands as shown in FIGS. 5 and 6, as oneembodiment.

In FIG. 12, the elongated member 130 is tapered such that thecross-sectional area S_(go) is a maximum at the proximal end 136interfacing with the transition segment 134 and is a minimum S_(c), atthe tip 132. An area function is defined as N where N−S_(go)/S_(c), andis the area ratio of the Gaussian portion, and it establishes gain. Theultrasonic wave is supported by particle motion in the titanium. Theparticles are vibrating about their neutral position in a longitudinalor extensional wave. The particles do not move along the length of thehorn, but only vibrate, just as a cork or bobber shows that a wavepasses through water via the liquid. As the horn wall thicknessdecreases, more strain occurs in the metal as the particles move agreater distance about their neutral position. The displacement of theend of the horn is due to strain along the horn. All the particlessupporting the wave are moving at the same resonant frequency. Thegreater the strain, the greater the velocity of the particles necessaryto maintain the same frequency.

Mechanical gain in the ultrasonic horn 100 is maximized withinacceptable stress limits of the titanium with stepped horn, Gaussianhorn, blended short straight section, and flared exponential profiles.CUSA® (Integra Life Sciences Corporation, Plainsboro, N.J.) Ampulla(Gaussian) profile affords multiplying the gain of the stepped horn witha uniform distribution of stress, and this profile coupled with a blendto short straight section and flared exponential provide high-gain andforward propagation of ultrasound with minimal errant reflection orstanding waves that could limit transmitted ultrasound, increase powerrequirements, or reduce horn stroke amplitude. These horn profilespromote high mechanical gain, forward propagation of ultrasound, andcommensurate surgical tip distal-end stroke.

Stroke amplitude was not sacrificed in adapting to a larger wallthickness distal end for 36 kHz shear stress tip; in fact, prototypehorn stroke exceeded the commercial baseline. This was accomplished withoptimization of the Gaussian profile and blend to the straight section.Stroke peak-to-peak of the prototypes was 196 pm (0.0077 in) versus 183pm (0.0072 in).

In one embodiment, pre-aspiration apertures or holes 150 (FIG. 1) areformed through opposing sides of the elongated member 130 wall onopposing sides of a straight or constant diameter portion.Pre-aspiration apertures may be employed in conjunction with theinternal channel 146, which, as previously noted, extends from theproximal end 104 to the distal tip 132. The pre-aspiration holes 150 canbe optionally used to suction a portion of the irrigation liquidemployed through the channel to aid in cooling the tip. Thepre-aspiration holes can also reduce misting caused by cavitation at thedistal end of tip, thereby improving viewing via endoscopes ormicroscopes.

In terms of applications, the ultrasonic horn 100 is useful forcranial-based surgery, and when performing trans-sphenoidal orendoscopic-nasal approaches. The ultrasonic horns 100 and 101 of thepresent disclosure can be combined with irrigation and aspirationsystems such as is disclosed in, for example, FIG. 3 of U.S. Pat. No.6,214,017 B1 to Stoddard et al., which as noted is incorporated byreference herein in its entirety. Irrigation in the internal channel 146aids in cooling the material of the horn which is in flexure.Pre-aspiration holes 150 may also aid in cooling. The cooling capabilitycan be enhanced by suctioning some portion of the irrigation liquidthrough the internal channel 146 of the horn 100 or 101 viapre-aspiration.

As used herein, “vacuum” is meant to include partial vacuum or loweredpressure. The term “angled inwardly” is meant to indicate that the angleis formed on the inside surface of the contact annulus. The term “angledoutwardly” is meant to indicate that the angle is formed on the outsidesurface of the contact annulus. Additionally, the term “lands” is meantto refer to the surface commonly given this name in the art and is alsomeant to refer to other surfaces that perform the same function.

The word “comprise” and variations thereof, such as, “comprises” and“comprising” are to be construed in the normal patent law sense; i.e.,an open, inclusive sense, which is as “including, but not limited to.”

While the present invention has been described herein in terms ofcertain preferred embodiments, those skilled in the art will recognizethat modifications and improvements may be made without departing fromthe scope of the invention. Moreover, while individual features of oneembodiment of the invention may be discussed or shown in the drawings ofthe one embodiment and not in other embodiments, it should be apparentthat individual features of one embodiment may be combined with one ormore features of another embodiment or features from a plurality ofembodiments.

1. An ultrasonic horn configured for use with an ultrasonic surgicalhandpiece having a resonator that generates ultrasonic waves, theultrasonic horn comprising: a body member having a proximal end, adistal end, and a longitudinal axis, the proximal end being adapted toconnect to the handpiece and receive ultrasonic waves from thehandpiece, and the body member configured to conduct the receivedultrasonic waves to the distal end; and an ultrasonic blade located atthe distal end, the ultrasonic blade being non-annular and having alinear cutting surface on which are located a first row of a pluralityof teeth and a second row of a plurality of teeth, the cutting surfaceconfigured so that the first row and the second row of teeth are locatedside by side one another and both first and second rows are parallel tothe longitudinal axis, each tooth of the pluralities of teeth in thefirst and second rows having a root located at the cutting surface, apeak, and a land located outward from the cutting surface, each landconfigured to propagate ultrasonic waves outwardly from the distal end;wherein the teeth in the first row are located and oriented in relationto the teeth in the second row on the cutting surface so that ultrasonicwaves propagated outwardly by lands of teeth of the first row intersectultrasonic waves propagated outwardly by lands of teeth of the secondrow to create shear stress fields; wherein roots of the first row ofteeth are located transverse to the longitudinal axis to roots of thesecond row of teeth and peaks of the first row of teeth are offset frompeaks of the second row of teeth transverse to the longitudinal axis. 2.The ultrasonic horn of claim 1 wherein the linear cutting surface has afirst width on which adjacent teeth are located, and wherein the bladehas material under the linear cutting surface that is undercut wherein awidth of the blade at the undercut is less than the first width of theblade at the linear cutting surface.
 3. The ultrasonic horn of claim 1wherein the first row of a plurality of teeth is located on the cuttingsurface with lands extending in the distal direction.
 4. The ultrasonichorn of claim 1 wherein roots of the first row of a plurality of teethare transversely aligned with roots of the second row of a plurality ofteeth across the longitudinal axis at the cutting surface.
 5. Theultrasonic horn of claim 4 wherein an angle of the lands of the firstrow of a plurality of teeth is different from an angle of the lands ofthe second row of a plurality of teeth.
 6. The ultrasonic horn of claim1 wherein roots of the first row of a plurality of teeth are offset fromroots of the second row of a plurality of teeth across the longitudinalaxis at the cutting surface.
 7. The ultrasonic horn of claim 6 whereinan angle of the lands of the first row of a plurality of teeth isdifferent from an angle of the lands of the second row of a plurality ofteeth.
 8. The ultrasonic horn of claim 7 wherein an angle of the landsof the first row of a plurality of teeth is opposite an angle of thelands of the second row of a plurality of teeth.
 9. The ultrasonic hornof claim 1 wherein the first row of a plurality of teeth is located atthe cutting surface and oriented at an angle to the longitudinal axis sothat ultrasonic waves propagating from lands of the first row of aplurality of teeth intersect ultrasonic waves propagating from lands ofthe second row of a plurality of teeth wherein a shear field is locatedtransverse to the longitudinal axis.
 10. (canceled)
 11. The ultrasonichorn of claim 1 wherein the lands of the teeth in the first row of aplurality of teeth extend in the distal direction and the lands of theteeth in the second row of a plurality of teeth extend in the proximaldirection.
 12. (canceled)
 13. The ultrasonic horn of claim 1 wherein thefirst and second rows of pluralities of teeth are parallel with thelongitudinal axis and are positioned on either side of the longitudinalaxis in forming the linear cutting surface of the blade.
 14. Theultrasonic horn of claim 1 wherein the roots of the teeth in the firstrow of a plurality of teeth are offset from the roots of the teeth inthe second row of a plurality of teeth and the lands of the first row ofa plurality of teeth have the same but opposite angle in respect to thelands in the second row of a plurality of teeth.
 15. An ultrasonic hornconfigured for use with an ultrasonic surgical handpiece having aresonator that generates ultrasonic waves, the ultrasonic horncomprising: a body member having a proximal end, a distal end, and alongitudinal axis, the proximal end being adapted to connect to thehandpiece and receive ultrasonic waves from the handpiece, and the bodymember configured to conduct the received ultrasonic waves to the distalend; and an ultrasonic blade located at the distal end along thelongitudinal axis of the body member, the ultrasonic blade beingnon-annular and having a linear cutting surface on which are locatedfirst and second parallel linear rows of teeth, each row having aplurality of teeth, the first and second rows being positioned on eitherside of the longitudinal axis adjacent each other, each tooth having aroot located at the cutting surface and a land located outward from thecutting surface, each land configured to propagate an ultrasonic waveoutwardly; wherein the lands of the first row of teeth and the lands ofthe second row of teeth are located and oriented in relation to eachother so that the respective ultrasonic waves propagated outwardly bythe lands of one row intersect with the ultrasonic energy propagatedoutwardly by the lands of the other row to create shear stress fields.16. The ultrasonic horn of claim 15 wherein: the locations of the rootsin the first linear row of teeth are offset from the locations of theroots in the second linear row of teeth transverse to the longitudinalaxis.
 17. The ultrasonic horn of claim 15 wherein: the locations of theroots in the first linear row of teeth are aligned with the locations ofthe roots in the second linear row of teeth transverse to thelongitudinal axis.
 18. A method of creating a shear stress field withultrasonic waves, comprising: conducting ultrasonic waves through a bodymember from a proximal end of the body member to a distal end of thebody member, the body member having a longitudinal axis; and propagatingthe conducted ultrasonic waves outwardly from the distal end of the bodymember through a first row of teeth and a second row of teeth with thefirst and second rows of teeth both mounted to a cutting surface of anon-annular blade located at the distal end and are positioned adjacenteach other, each tooth having a root located at the cutting surface anda land located outward from the cutting surface; wherein the step ofpropagating comprises propagating ultrasonic waves outwardly by lands ina direction that intersects propagated ultrasonic waves from other landsto thereby form shear stress fields.
 19. The method of creating a shearstress field of claim 18 wherein the propagating step further includespropagating the conducted ultrasonic waves outwardly from the distal endof the body member through lands of the first row of teeth and throughlands of the second row of teeth, wherein the first and second rows ofteeth are located separately at the non-annular cutting surface and arepositioned adjacent each other in a side-by-side arrangement across thelongitudinal axis.
 20. The method of creating a shear stress field ofclaim 19 wherein the lands of one row of teeth have a first angle andthe lands in the other row of teeth have a second angle that is oppositethe first angle.
 21. The ultrasonic horn of claim 15 wherein the linearcutting surface has a first width on which the adjacent first and secondparallel linear rows of teeth are located, and wherein the blade hasmaterial under the linear cutting surface that is undercut; whereby awidth of the blade at the undercut is less than the width of the bladeat the cutting surface.
 22. The ultrasonic horn of claim 17 wherein thelands of the first parallel linear row of teeth have a different anglefrom the lands in the second parallel linear row of teeth.